This is standard Reformed theology. The 17th-century Reformed orthodox spoke regularly about a sort of covenant of works with national Israel. It wasn’t a well-formed or highly defined doctrine but they appealed to the promulgation of the law at Sinai as proof of the pre-lapsarian covenant of works. The fact that some folk today consider any version of a covenant of works with Israel to be a symptom of dispensationalism illustrates the state of ignorance about the history of Reformed federal theology. There was never any doubt in Reformed orthodoxy about how believing Israelites were justified: sola gratia, sola fide. As Protestants they understood the difference between grace and works (or between grace and cooperation with grace). They understood that Adam would have been glorified had he kept covenant and that, because he had not sinned, he could keep covenant unto glorification. They also understood that sinners cannot keep covenant for salvation or justification. They saw in the legal language used with Israel a reflection of the pre-lapsarian covenant of works.
At least one strand of modern biblical scholarship argues that there were two sorts of covenants in the world in which Scripture was given, a suzerain-vassal treaty, which was a sort of covenant of works (“do this and live”) and the second was a royal grant covenant (“I will be a God unto you and to your children”). Thanks to Pastor Shane Lems at the Reformed Reader for reminding us of the work of Levenson and Weinfeld. Mike Horton has tapped into this research as part of his exposition of Reformed covenant (federal) theology, God of Promise.